1. FIELD OF THE INVENTION
This invention relates to sliding structures for a high load, and more particularly to sliding parts working under a high load such as a bushing sleeve of a toggle type mold clamping apparatus of an injection molding machine or a die-casting machine.
2. DESCRIPTION OF THE RELATED ART
In a mold clamping apparatus of an injection molding machine or a die-casting machine, a guide mechanism for opening and closing a mold or a toggle mechanism for clamping a closed die with high pressure has previously been used.
In rotative sliding parts of the toggle mechanism or in reciprocating sliding parts of the guide mechanism, steel or cast iron bushing sleeves are used. Steel or cast iron is used to increase the bushing sleeves withstandability to a high load caused by the high pressure clamping of the mold. The above mentioned rotative sliding parts or reciprocating sliding parts are required to have increased lubricativeness to make the mold open/closed smoothly. To this end, not only lubrication by supplying oils and fats but also non-oil supply type lubrication by a solid lubricating material has been practiced in recent years. As with oil-supply lubrication, automatic oiling by the connection of the automatic oiling apparatus is practiced in addition to periodical greasing by hand work.
On the other hand, there are the non-oil supply type lubrication systems. Granulated solid lubricating can be used for non-oil supply type lubrication. For example, graphite, can be embedded in a metal material of the bushing sleeve.
However, the oil supply type lubrication described above has the problem that the lubricating oil leaks out of the sliding parts to stain their surroundings or adheres to the moldings to stain them.
Furthermore, as the troublesomeness of the periodical maintenance is unavoidable in the manual lubrication, there is a danger of shortage of the lubricativeness due to a limited of lubrication supply. Also, in the case of the automatic lubrication, there is a danger of insufficient lubricativeness if the supply of lubricating oil is inadequate due to incorrect adjustment. Such poor lubrication would cause abrasion or malfunction of the sliding surfaces.
In the non-oil supply lubrication described above, there is the problem that the lubrication is limited to the granular parts of the solid lubricating material. The bushing sleeve cannot get enough lubricating performance if the metal material exposed around the granular material is a material of low lubricativeness such as a steel material.
In the case of using a bushing sleeve made of copper or the like which has high lubricativeness, there is the problem that its strength is insufficient and the respective members of the mold clamping device cannot resist a high load up to 1000-1300 kgf/cm.sup.2.
It is an object of the present invention to provide a high load sliding structure, which has high strength, ensures sufficient lubrication, and is easy to handle and prevents staining of the surroundings.